ESPN reported last week that Barca and United had reached an agreement over a transfer worth an initial €65 million rising to €85m, although the make-up of the add-ons remained a source of discussion.
However, Laporta said on Saturday that he would do all he could to retain De Jong's services, and he repeated the same message at the presentation of new signing Franck Kessie on Wednesday.
"Frenkie is a Barcelona player and, save there was the need to let him go him, he is not available," Laporta said.
"We do not want to sell him. There are offers for him and if at any moment it was in our interests, we could do a deal, but that is not the case. We don't want to sell him."
Throughout United's pursuit of De Jong, sources have told ESPN that the player's preference is to remain at Barca, who he joined from Ajax in 2019.
Reports in Spain have said Barca would like De Jong to take a pay cut as they attempt to bring their wage bill down, but sources have told ESPN the Dutch international is unlikely to do so.
De Jong, 25, previously agreed a salary cut when he penned a new deal in 2020 and, over the last 18 months, has earned significantly less than he should have with the promise he will be compensated over the final four years of his deal, which expires in 2026.
Meanwhile, Laporta said a contract offer remains on the table for Ousmane Dembele, who has technically been a free agent since his Barca deal expired last week.
Laporta said there is "no deadline" for the French winger to decide his future and that his camp "want to keep talking."
The Barca chief also expressed optimism that the club will be able make further signings once they have sold a further 15% of their television rights.
AC Milan midfielder Kessie and Chelsea defender Andreas Christensen have both signed on free transfers this week, and sources have told ESPN that Bayern Munich's Robert Lewandowski, Leeds United's Raphinha and Sevilla's Jules Kounde remain targets.
Barca sold 10% of their domestic TV rights for €207.5m last week, but the club still need to bring in more capital to be able to operate outside of LaLiga's tough financial restrictions.
"We are working on further signings which can be executed when further commercial deals are in place," Laporta added.
"I won't give a number in terms of how many players will come in. What I will say is we will have a more competitive team next season with the players we have signed and those we will sign."
Barca have also been linked with Cristiano Ronaldo. Sources told ESPN that Ronaldo has requested to leave United, but Laporta would not confirm if he's been offered to the club after meeting with the player's agent, Jorge Mendes, on Monday.
United remain in the dark about Ronaldo's plans for preseason with the club set to compete in a tour of Thailand and Australia ahead of the 2022-23 campaign.
"I won't speak about individual players, it's not in Barca's interests to do so," Laporta said.
"It is true I [had dinner with Mendes] this week. He represents a lot of players, so it is always good to meet with him to get an idea of how the transfer market is."